We've been playing this variant for some time now (we'll over 20 games) and have found it to provide greater depth, more tension and turn angst, and far more interesting play. The changes are as follows:
1) The game no longer ends when a player had placed all their dolmens (square blocks).
2) When an area is compleatly surrounded it is scored immediately and the scoring dolmens (square blocks) are returned to their players. Returned dolmens may then be placed in the normal fashion on future turns.
3) The game ends when any player has placed all of their stones (octagonal prisms), with each other player having one more turn after that point.
That's it.